For a polymerase chain reaction (PCR) or the like, it is required to denature double strands of DNA or the like prepared from a sample to single strands. Conventionally, as a method for denaturing double strand nucleic acids to single strand nucleic acids, thermal denaturation has been mainly used which utilizes the property of the hydrogen bonding between the nucleic acid bases of a double strand nucleic acid of being cut by heat.
For example, the typical thermal denaturation in a PCR method adds heat to a sample including a DNA at approximately 90 to 95° C. and dissociates the double strand nucleic acids to single strand nucleic acids. Subsequently, in the annealing step, the sample is cooled to approximately 50 to 65° C. so as to anneal with a primer that is complementary to the DNA, and in the elongation step, the sample is heated to approximately 70 to 72° C. to elongate, starting from the primer, a strand that is complementary to the single strand with the use of a polymerase (e.g., refer to WO 2008/057375 A (JP-2010-508813 A)). These steps are typically repeated 25 to 40 times.
Therefore, it is necessary for the activity of a DNA polymerase used for a PCR to be maintained in the thermal cycles, in particular in a high temperature range from 90 to 95° C.
Alternatively, it is also conventionally carried out to denature double strands of DNA to single strands with alkali. This utilizes the property of double strands of DNA of dissociating and denaturing to single strands in an environment having a pH of 10 or more.